This invention relates to a replaceable filter cartridge for use in a gravity-fed water treatment system. In particular this invention relates to a novel structural filter cartridge for a carafe/pitcher system in an air vent facilitates water flow and in which only the carbon block is replaceable.
Carafe/pitcher water filtration systems are batch treatment and filtration devices in which water is filtered, treated and stored in a container. The treated water is discharged from a spigot on the container, providing a self-contained water treatment system. These self-contained systems typically have upper and lower chambers separated by a filter cartridge.
The water treatment process relies on gravity to force water through the filter cartridge to remove harmful contaminants from the water. The upper chamber receives untreated water to be filtered while the lower chamber receives and stores the filtered water. The water is forced through the filter cartridge by gravity.
The presence of unwanted and potentially harmful contaminants in drinking water are a cause for health concern. As such, there is a desire for water treatment devices suitable for use in the home and as portable instruments for water treatment. As a result, many water treatment devices and methods have been developed to remove contaminants or otherwise treat the water to obtain a suitable drinking water.
Some of these water treatment devices and methods utilize treatment materials, which, of their own nature, can be distasteful to consumers of the treated water. For example, municipal water treatment facilities use chlorine as an active agent to remove bacterial contaminants but the odor and taste of the treated water can be offensive. It is known to use activated carbon to treat water to remove the offensive odor and taste of chlorine-treated water, however, the flow rate of water through the activated carbon can be hampered. When the life of the carbon has been exhausted, the entire cartridge, that is the plastic housing containing the carbon is discarded along with the carbon.
In addition to chemical and particulate contaminants, several types of harmful contaminants in drinking water are a cause for health concern. Even municipal water treatment fails to adequately remove all of the hazardous contaminants. Most municipal systems use chlorine as disinfectant to remove bacteria. It is known that excess chlorine normally used by the municipality is in itself a source to create harmful chemicals commonly known as disinfectant by products, (DBP). These DBP, along with herbicides and pesticides, often present and known as volatile organic chemicals (VOCs), are harmful chemicals in the water system. Besides these volatile organic chemical contaminants, biological contaminants including protozoan cysts as Giardia lamblia and Cryptosporidium, excreted by animals, are present in certain waters.
Cysts are not easily removed by conventional oxidizing agents. Common methods of removing cysts are to trap them in a filter that has a porosity less than 2 microns. Such filters with pore sizes less than 2 microns typically are used in water purification systems that use high water line pressure.
Gravity filtration is one of the oldest ways of filtering water. Starting from a simple filter cloth to remove suspended impurities to carbon granules along with certain ion exchange media to remove chlorine and certain heavy metals, gravity filtration systems have upper and lower chambers separated by filter cartridge. The system relies on gravitational forces acting on the untreated water in the upper chamber to force the water through the cartridge and into the lower chamber to produce filtered water.
Gravity filtrations systems in residential use vary in sizes, defined by the capacity of the two chambers. One such gravity filtration system in common residential use is the carafe type of filter with the top container having a capacity less than 3 liters. The pressure of the untreated water is sufficient to force the water through a limited amount of activated carbon granules and ion exchange resins.
Replaceable filter cartridges for household use are known. In one device, a filter cartridge contains particles of activated charcoal and carbon or other suitable absorbent material. Water is filtered by passing it through the tubular wall of the cartridge from the space between the cartridge and the housing toward the inside of the tubular cartridge. The filter cartridge is generally cup-shaped and the cartridge structure provides a long flow path for water traveling from the inlet to the outlet. This provides effective odor and taste filtering of the water due to the long contact time.
In another system, a filter tube has a plurality of randomly disposed glass fibers having interstices to define the porosity of the filter. The glass fibers are bonded at the junctions of the fiber cross-overs with a hardened silicone resin bonding agent. However, the bonding agent can impart hydrophobicity to the filter and restrict the scope of the filter applications in that organic bonding agents can have a color, which darkens with sunlight and use.
Another system discloses a pass-through pitcher filter that has a compact filter element including a thin annular disk of molded granular activated carbon and a peripheral annular seal element. The seal element allows the filter to be replaceably mounted on the lower end of an upper plastic reservoir, and the reservoir is adapted to be supported in the top of a pitcher for receiving filtered water. The plastic reservoir and filter are placed on a pitcher for receiving and dispensing the treated water. This assembly relies on gravity flow of water from the reservoir to the pitcher via the filter. The seal element utilizes a synthetic rubber material and is preferably molded around the carbon filter disk.
The filter element is made from a rigid sintered block of activated granular carbon and includes a suitable binder, such as polyethylene, compressed and heated to form a molded porous block. An annular synthetic rubber seal is attached to the periphery of the carbon block. However, when the filter element is used initially or after it has remained unused for a period of time, surface tension between water in the reservoir which is to be filtered and the dry porous carbon block may inhibit normal gravity flow of the water through the filter element. To initiate flow, manual pressure is applied to a bellows element of the reservoir to compress air in the reservoir to force water through the carbon block to initiate water flow.
Yet another system includes a filter cartridge for a gravity-fed water treatment device that has a hydrophilic porous particulate filter with an interior volume filled with granular filter activated carbon, an ion exchange resin or a combination of granular carbon and resin. The porous particulate filter is microporous and has a pleated sheet filter media, and is arranged to establish with a pressure of about 0.5 pounds per square inch (psi) a flow rate of water by gravity through the filter cartridge.
Such a device has a low flow rate, which is not practical for a gravity fed water treatment device. To overcome the low flow rate, the porous particulate filter contains a hydrophilic material. Moreover, such a device does not typically remove volatile organic chemicals, and it is not capable of doing so without specified treating chemicals or materials.
Accordingly, there is a need for a water filter having improved fluid flow over known filters. Desirably such a filter has a removable filter medium adapted for field removal, cleaning, and replacement. More desirably, such a filter is capable of removing harmful chemicals known as disinfectant by-products (DBP) and volatile organic chemicals (VOC) and protozoan cysts, as well as heavy metals such as lead, cadmium and mercury. More desirable still, such a water filtering system uses carbon block filters that are bio-static such that any trapped bacteria will not multiply and grow.